1. Field of the Invention
This invention relates to the testing of electronic circuits, and more specifically the testing of integrated circuits.
2. Description of the Related Art
As electronic circuits become more complex, test requirements to ensure their reliability and functionality become more demanding. This is particularly true of integrated circuits. As integrated circuits (ICs) have advanced, both pin counts and transistor counts have increased dramatically, thereby placing greater demands on testing methods to ensure their reliability. In addition to integrated circuits becoming more complex, system boards upon which many ICs are implemented have become more complex as well.
Characterization testing is one type of testing commonly performed on integrated circuits, both in the design verification stage as well as the production stage. Characterization testing may include various test methods to ensure that a device under test (DUT) meets electrical specifications. In a typical characterization test, the DUT will be coupled to a printed circuit board (PCB) known as a load board, which is then coupled to an automated test system. The automated test system may provide various electrical stimuli to the DUT, through the load board. The test system may then observe the response of the DUT to the various electrical stimuli, comparing the responses with predefined electrical specifications in order to determine whether the device has passed or failed.
System level or functional testing is another type of testing performed on ICs. This type of testing may occur after a given IC has been mounted to a printed circuit board, or other type of carrier. For example, the IC may be an ASIC (application specific IC) that is mounted on a system board. When assembly of the system board is complete, the board may undergo testing to ensure that it functions as required. This may include testing the ability of the ASIC to communicate correctly with the various other chips on the board, as well as with an environment to an external board (e.g. a daughter card coupled to the system board).
Discrepancies may arise between characterization testing and system level testing. For example, an IC may successfully pass all characterization tests, but may still be unable to function properly on a system board. These discrepancies may be exacerbated by tolerance stack ups on both the IC and the system board, or other electrical factors that were not considered during the characterization testing.
The problems of testing IC's may be particularly acute for those IC's configured for source synchronous I/O. In an IC configured for source synchronous I/O, a clock signal is transmitted along with a data transmission in order to ensure that the data is synchronized at the receiver. Because of the high speeds at which source synchronous devices operate, clock skew and other factors may play a significant role in determining their operability on a system board. As such, the margin of operation in a characterization test for a source synchronous IC may be extremely small.